Mapping Alexis' genetic code led to a new prescription that has the Encinitas, Calif., girl back to running track and changed her twin brother's care, too.

It's one of the first examples of using genome sequencing to directly benefit a patient rather than just to study the causes of disease.

The research, reported Wednesday by scientists at Houston's Baylor College of Medicine, doesn't mean DNA mapping is ready for your doctor's office.

We all have a lot of glitches in our genome, and "being able to zero in on the one that matters is not a trivial experience," National Institutes of Health Director Dr. Francis Collins cautioned.

Still, he called the research a step toward more real-world use.

"It's not just a curiosity," said Collins, whose agency helped fund the work. "This is the leading edge of what will become, pretty soon, a deluge of such reports."

Frustrated patients will drive that demand as the price of a personal genome map drops, predicts Dr. James Lupski, Baylor's vice chairman of genetics.

The first draft of a human genome in 2000 cost about $3 billion and a decade of government research. A year ago, it cost about $30,000 each to sequence the genomes of Alexis and her brother, plus about $40,000 more in computer and specialist analysis to be sure they'd identified the right gene flaw, said study co-author Dr. Richard Gibbs, who directs the Baylor Human Genome Sequencing Center.

NIH's Collins said an uncomplicated genome sequencing can cost as little as $8,000 today — and many experts believe the price may drop to less than $1,000 in a few more years.

Alexis and her twin Noah are no strangers to the hurdles of diagnosis. At age 2, doctors concluded cerebral palsy explained their movement problems. But by 5½, their mother, Retta Beery, suspected something else. Alexis would wake up able to walk but by late morning couldn't even sit up or use her arms.

Beery read about a different disease named dopa-responsive dystonia, a neurological disorder that causes muscles to spasm and twist. It mimics some of cerebral palsy's symptoms but has those daytime fluctuations — and is treatable with the Parkinson's drug levodopa. Sure enough, the twins' muscles began working so normally that over the next few years they played softball and basketball and ran track.

But about 18 months ago, Alexis developed a nighttime cough that progressed to wheezing. She had to give up sports. At one point, her mother said, she quit breathing and paramedics had to revive her. Specialists were baffled. The family wound up at Baylor after Retta Beery heard about genomics through her husband's job at a company that makes equipment used in genetics research.

Genome sequencing so far has been used mainly to find genes connected with different diseases, not for personal benefit but in hopes of developing new drugs or single-gene tests used for diagnosing illness. The problem: Most diseases aren't caused by one or two bad genes.

Baylor, known for research into personal genome sequencing, discovered that was Alexis' problem. The two best-known gene culprits weren't causing her dystonia. It was a different genetic mutation that lowered her body's levels of another brain chemical, serotonin, as well as dopamine, scientists reported in the journal Science Translational Medicine.

With that finding, doctors added to Alexis' daily treatment a serotonin-producing medication that stopped her airway spasms and let her get back to sports. Noah had the same gene defect despite no breathing problems, but the twins' mother says the medication helped improve his hand-eye coordination and ability to focus.